The present invention relates generally to a single pass full color printing system consisting generally of a raster output scanner (ROS) optical system and a quad-level xerographic unit and a tri-level xerographic unit in tandem, and more particularly, to a specific sequence of toners for such a single pass full color printing system which permits ease of exposure of the photoreceptor through toner already deposited upon the photoreceptor.
A single pass full color printing system can consist of a raster output scanner (ROS) optical system and a quad-level xerographic unit and a tri-level xerographic unit, as described in U.S. Pat. No. 5,221,954, commonly assigned to the same assignee as the present application and herein incorporated by reference. In that printing system, a photoreceptor belt is uniformly charged, then exposed to the first beam from the raster output scanner (ROS) optical system which produces four charge levels on the photoreceptor belt. The quad-level xerographic unit will then deposit toner of a first color, toner of a third color, toner of a combination of a second and the third color, or no toner upon the photoreceptor belt based upon the charge level. The photoreceptor belt is then recharged and re-exposed to a second beam from the raster output scanner (ROS) optical system which produces three new charge levels on the photoreceptor belt. The tri-level xerographic unit will then deposit toner of a fourth color, toner of a fifth color, or no toner upon the photoreceptor belt based upon the charge level. The colored toners upon the photoreceptor belt are then transferred to a sheet of material and fused to the sheet. The photoreceptor belt is then cleaned of residual toner and charges.
In the prior art reference, the colored toners of cyan and magenta are deposited upon the photoreceptor belt by the first xerographic unit. Red or infrared light is commonly used in xerographic systems to expose the photoreceptor belt to produce charges on the belt. It is difficult for the second red or infrared beam to pass through the already deposited cyan and magenta toners to expose the recharged photoreceptor belt so that the second xerographic unit can deposit further colored toners.
It is an object of this invention to provide a single pass full color printing system using a quad-level xerographic unit and a tri-level xerographic unit which permits ease of exposure of the photoreceptor through toner already deposited upon the photoreceptor.